Perpendicular magnetic recording medium and method of manufacturing the same

ABSTRACT

A vertical magnetic recording disc ( 100 ) includes a base ( 10 ), a magnetic recording layer ( 22 ), and a medium protection layer ( 26 ). The magnetic recording layer ( 22 ) is a ferromagnetic layer having a granular structure where a granular portion is formed. The medium protection layer ( 26 ) contains nitrogen (N) atoms and carbon (C) atoms with a number ratio (N/C) in a range from 0.050 to 0.150. In a Raman spectrum obtained by exciting the medium protection layer ( 26 ) by argon ion laser light of wavelength 514.5 nm, from which a fluorescence is removed, the peak ratio Dh/Gh is in a range from 0.70 to 0.95, when a D peak Dh appearing in the vicinity of 1350 cm −1  is separated from G peak Gh appearing in the vicinity of 1520 cm −1  by the Gauss function.

TECHNICAL FIELD

The present invention relates to a perpendicular magnetic recordingmedium that is loaded on, for example, an HDD (hard disk drive) using aperpendicular magnetic recording system and also relates to a method ofmanufacturing the medium.

BACKGROUND ART

In accordance with the recent increasing storage capacity in informationprocessing, various types of information recording technologies havebeen developed. In particular, the surface recording density of an HDDusing a magnetic recording technology has been increasing at an annualrate of about 100%. Recently, 2.5-inch-diameter perpendicular magneticrecording disks used in HDDs and the like also have been required tohave an information recording capacity of larger than 100 GB per disk.In order to satisfy such a requirement, it is necessary to achieve aninformation recoding density of higher than 150 Gbits per square inch.

In order to achieve a high recording density in a perpendicular magneticrecording disk used in an HDD or the like, it has been necessary toreduce the size of crystalline magnetic particles constituting amagnetic recording layer for recording information signals andsimultaneously to decrease the thickness of the layer. However, in acase of a magnetic disk of a conventionally commercialized in-planemagnetic recording system (also called a longitudinal magnetic recordingsystem or a horizontal magnetic recording system), as a result of theprogress in the size reduction of crystalline magnetic particles,thermal stability of recorded signals is deteriorated by thesuperparamagnetic phenomenon. This causes a so-called thermalfluctuation phenomenon in which the recorded signals are erased. Thus,the reduction in size of crystalline magnetic particles has been afactor that inhibits an increase in recording density of the magneticdisk. In order to solve the inhibitory factor problem, recently, amagnetic disk of a perpendicular magnetic recording system(perpendicular magnetic recording disk) has been proposed.

In the perpendicular magnetic recording system, the axis of easymagnetization of a magnetic recording layer is adjusted so as to beorientated in the direction perpendicular to a surface of a substrate,unlike the case of the in-plane magnetic recording system. Theperpendicular magnetic recording system can suppress the thermalfluctuation phenomenon compared to the in-plane recording system and istherefore suitable for increasing the recording density.

In addition, in accordance with such an increase in the informationrecording density, both the linear recording density (BPI: bit per inch)in the circumferential direction and the track recording density (TPI:track per inch) in the radial direction are growing steadily.Furthermore, a technology for increasing the S/N ratio by narrowing thedistance (magnetic spacing) between the magnetic layer of a magneticdisk and the recording/reproduction element of a magnetic head has beeninvestigated. It is recently desired that the flying height of amagnetic head be 10 nm or less.

As one of technologies for thus reducing the magnetic spacing, a DFH(dynamic flying height) head has been proposed. In the DFH head, amagnetic head is thermally expanded by inducing heat in a magnetic headelement during the operation of the element so as to slightly protrudein the ABS (air bearing surface) direction. By doing so, the distancebetween the magnetic head and the magnetic disk is controlled so thatthe magnetic head can constantly and stably fly with a narrow magneticspacing.

The perpendicular magnetic recording disk has a medium-protecting layerfor protecting the surface of a magnetic recording layer from beingdamaged when the magnetic head crashes with the perpendicular magneticrecording disk. The medium-protecting layer forms a carbon overcoat(COC), i.e., a coating with a high degree of hardness due to a carboncoating. Furthermore, in some medium-protecting layers, both harddiamond-like bonds of carbon and soft graphite bonds of carbon arepresent (for example, Patent Document 1). In addition, a technology forproducing a diamond-like bond protection film by a CVD (chemical vapordeposition) method is disclosed (for example, Patent Document 2).Furthermore, a technology for enhancing durability of amedium-protecting layer is disclosed (for example, Patent Document 3).

Incidentally, in the perpendicular magnetic recording system, asingle-pole-type perpendicular head is employed to generate a magneticfield in the direction perpendicular to the magnetic recording layer, asdescribed above. However, since the magnetic flux emerging from asingle-pole end is prone to promptly return to a return magnetic pole onthe opposite side, a magnetic field with a sufficient intensity cannotbe applied to the magnetic recording layer by using only thesingle-pole-type perpendicular head. Therefore, a soft magnetic layer isprovided under the magnetic recording layer of the perpendicularmagnetic recording disk and is used as a path for the magnetic flux.This makes it possible to apply a perpendicular direction magnetic fieldwith a high intensity to the magnetic recording layer.

In addition, a technology preventing the occurrence of spike noise isalso known (for example, Patent Document 4). In the technology, the softmagnetic layer is separated into two layers with a spacer layer suchthat the directions of magnetization are parallel to the perpendicularmagnetic recording disk surface and are opposite to each other, that is,to form a so-called AFC (antiferromagnetic exchange coupling) structure.This prevents the occurrence of an enormous magnetic domain in ahorizontal direction in the soft magnetic layer and the occurrence ofthe spike noise due to the leaked magnetic flux in the perpendiculardirection, which is generated from the magnetic wall of the magneticdomain.

Furthermore, a lubrication layer is disposed on the medium-protectinglayer for protecting the medium-protecting layer and the magnetic headfrom the crash of the magnetic head. The lubrication layer is formed by,for example, applying and sintering perfluoro polyether.

[Patent Document 1] JP-A-H10-11734

[Patent Document 2] JP-A-2006-114182

[Patent Document 3] JP-A-2005-149553

[Patent Document 4] JP-A-2002-358618

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

In order to achieve the above-described magnetic spacing of, forexample, 10 nm or less, the medium-protecting layer of a perpendicularmagnetic recording disk is required to reduce the thickness thereof to 3nm or less. However, a simple reduction in the thickness of themedium-protecting layer causes deterioration in the durability, such aswear resistance and impact resistance, of the medium-protecting layeritself.

Various methods for forming the medium-protecting layer have beenconventionally known. However, since the durability of the conventionalmedium-protecting layers is insufficient, in a perpendicular magneticrecording disk apparatus of an LUL (load unload) system, an impact whena magnetic recording head is loaded on the perpendicular magneticrecording disk causes a slight scratch or the like on the perpendicularmagnetic recording disk. This leads to a problem of a decrease in thereproduced signal.

Furthermore, in also the case of using the above-described DFH head,when a magnetic head is brought into contact with a magnetic disk, alubrication layer material may be picked up by the magnetic head if thebonding strength of the lubrication layer is low. As a result, themagnetic head is covered with the picked up material. This may causeread/write faults or a high fly write phenomenon due to unstable flyingheight of the magnetic head. The high fly write is a phenomenon in whichdata that should be written to a magnetic disk has not been writtenbecause the magnetic head departed from the magnetic disk and causes areadout error even if the hardware is not broken.

In also the above-mentioned Patent Document 3, a technology forenhancing the durability of such a medium-protecting layer is described.However, no specific method for solving the problem of high fly write orreducing the thickness of the medium-protecting layer to 3 nm or lessare mentioned.

In addition, corrosion is one of problems conventionally involved inmagnetic media. The corrosion is a phenomenon, typically, in which ametal such as cobalt (Co) is precipitated from a lower layer and formsan oxide thereof on a surface of the medium-protecting layer. Thecorrosion erases the data recorded at the position where the corrosionoccurred and, in combination with a low flying height of the magnetichead, causes crash failure, which possibly develops into failure in thedisk drive.

The present inventors have conducted intensive investigation for solvingthe problems and have found that heat treatment of a magnetic layerimmediately before the formation of a medium-protecting layer changesthe properties of the medium-protecting layer formed immediately afterthe heating, the Raman spectrum of the medium-protecting layer ischanged by controlling the temperature of the heat treatment, thebonding strength of a lubrication layer is affected by the amount ofnitrogen in the outermost surface of the medium-protecting layer, andthe number ratio (N/C) of nitrogen atoms and carbon atoms in theoutermost surface of the medium-protecting layer depends on a change innitrogen flow rate of a surface treatment layer. Therefore, durability,such as wear resistance and impact resistance, of the medium-protectinglayer can be enhanced by increasing the diamond-like bonds by heatingthe magnetic layer immediately before the formation of themedium-protecting layer. This makes it possible to inhibit theoccurrence of corrosion.

However, a soft magnetic layer is already formed before the formation ofthe medium-protecting layer, and the soft magnetic layer has theabove-described AFC structure. The AFC structure is weak to heat, andthe antiferromagnetic coupling strength of the upper and the lower twolayers disposed in antiparallel to each other is reduced by heating to ahigh temperature, and finally, the function as the AFC structure may belost. If the AFC structure of the soft magnetic layer is destroyed,noise from the soft magnetic layer is increased, resulting in adifficulty in the achievement of a high recording density.

The present invention has been accomplished in view of the problemsinvolved in the configuration of the conventional medium-protectinglayer, and an object of the present invention is to provide aperpendicular magnetic recording medium that has enhanced durability,such as wear resistance and impact resistance, and is able to avoidvarious problems, such as high fly write and corrosion, even if thethickness of the medium-protecting layer is reduced to 3 nm or less, bypreventing the pick up of a lubrication layer material to the magnetichead and to provide a method of manufacturing such a recording medium.

Means for Solving the Problems

In order to solve the above-mentioned problems, according to one aspectof the present invention, there is provided a perpendicular magneticrecording medium comprising a magnetic recording layer on a substrate,and a medium-protecting layer on the magnetic recording layer, whereinthe magnetic recording layer is a ferromagnetic layer of a granularstructure having grain boundaries formed by a non-magnetic materialamong crystalline particles grown in a columnar shape and containing atleast cobalt (Co); and the medium-protecting layer is composed of acoating that includes carbon as a main component and nitrogen containedin a surface layer at a number ratio (N/C) of nitrogen (N) atoms andcarbon (C) atoms of 0.050 to 0.150, and in a spectrum removedfluorescence from a Raman spectrum in wavenumbers of 900 to 1800 cm⁻¹obtained by exciting the medium-protecting layer with argon ion laserlight having a 514.5 nm wavelength, a peak ratio Dh/Gh when a D peak Dhappearing near 1350 cm⁻¹ and a G peak Gh appearing near 1520 cm⁻¹ arewaveform-separated by a Gaussian function is 0.70 to 0.95.

By the constitution of heating a magnetic layer immediately before theformation of the medium-protecting layer, the peak ratio Dh/Gh in aRaman spectrum can be controlled to 0.70 to 0.95, and the durabilitysuch as impact resistance, wear resistance, and corrosion resistance canbe enhanced. In addition, the problem of high fly write and the crash ofthe magnetic head can be avoided by regulating the ratio (N/C) to 0.050to 0.150.

The perpendicular magnetic recording medium is formed so as to have anantiferromagnetic exchange coupling (AFC) structure containing 30 to 70at % iron (Fe), and a soft magnetic layer having a saturationmagnetization Ms of 1.2 T or more may be provided under the magneticrecording layer. The soft magnetic layer is separated into two layerswith a spacer layer therebetween and is configured such that themagnetization directions are parallel to the disk surface of theperpendicular magnetic recording medium and are opposite to each other.In the thus configured antiferromagnetic exchange coupling (AFC:antiferromagnetic exchange coupling, hereinafter simply referred to asAFC) structure, the antiferromagnetic coupling strength of the upper andthe lower two layers disposed in antiparallel to each other is reducedby heating at a prescribed temperature or more. In the presentinvention, an AFC structure that is strong to heat is formed by mixingiron to the soft magnetic layer during the formation thereof, whichmakes it possible to conduct the heating immediately before theformation of the medium-protecting layer. In addition, the saturationmagnetization Ms affects the easiness of write to the recording medium,that is, affects the overwrite characteristics. A higher saturationmagnetization Ms achieves higher improvement of the overwritecharacteristics. Therefore, a constitution that provides a saturationmagnetization Ms of 1.2 T or more can maintain desired overwritecharacteristics.

Furthermore, the soft magnetic layer may have an exchange couplingmagnetic field Hex of 40O e or more. The coupling strength of the AFCstructure is determined on the basis of the exchange coupling magneticfield Hex. Therefore, a higher Hex indicates a stronger coupling of theAFC, and a Hex of lower than 40O e cannot maintain the function as anAFC structure.

The magnetic recording layer is formed so as to have a granularstructure, and a capped layer or an auxiliary recording layer may beprovided on the magnetic recording layer. Such a constitution can reducethe size of magnetic particles of the magnetic recording layer andenhance coercivity Hc. Therefore, the high-density recording propertiesand the low-noise properties of the magnetic recording layer can beenhanced. In addition, the perpendicular magnetic recording medium canbe further imparted with high thermal fluctuation resistance byproviding the capped layer on the magnetic recording layer.

The composition of the capped layer may be CoCrPtB. With this, a thinfilm showing a perpendicular magnetic anisotropy can be formed toenhance the high thermal fluctuation resistance of the perpendicularmagnetic recording medium.

In order to solve the above-mentioned problems, according to anotheraspect of the present invention, there is provided a method ofmanufacturing a perpendicular magnetic recording medium including amagnetic recording layer on a substrate, and a medium-protecting layercomposed of a coating including carbon as a main component on themagnetic recording layer, comprising forming a ferromagnetic layer of agranular structure having grain boundaries formed by a non-magneticmaterial among crystalline particles grown in a columnar shape andcontaining at least cobalt (Co), as the magnetic recording layer;heating the perpendicular magnetic recording medium such that in aspectrum removed fluorescence from a Raman spectrum of amedium-protecting layer formed later in wavenumbers of 900 to 1800 cm⁻¹obtained by exciting the medium-protecting layer with argon ion laserlight having a 514.5 nm wavelength, a peak ratio Dh/Gh when a D peak Dhappearing near 1350 cm⁻¹ and a G peak Gh appearing near 1520 cm⁻¹ arewaveform-separated by a Gaussian function is 0.70 to 0.95; forming themedium-protecting layer by a CVD method; and exposing themedium-protecting layer with nitrogen such that the number ratio (N/C)of nitrogen (N) atoms and carbon (C) atoms is 0.050 to 0.150.

By forming the perpendicular magnetic recording medium such that thepeak ratio Dh/Gh in a Raman spectrum is 0.70 to 0.95 and the ratio (N/C)is 0.050 to 0.150, the durability, such as wear resistance and impactresistance, is enhanced to enable avoidance of various problems such ashigh fly write even if the thickness of the medium-protecting layer isrestricted to 3 nm or less.

Before the formation of the magnetic recording layer, a soft magneticlayer having an antiferromagnetic exchange coupling (AFC) structurecontaining 30 to 70 at % iron (Fe) may be formed. The soft magneticlayer may have an exchange coupling magnetic field Hex of 40O e or more.

After the formation of the magnetic recording layer, a capped layerhaving a granular structure may be formed. The composition of the cappedlayer may be CoCrPtB.

The heating may be performed at a temperature of 157 to 204° C. When theheat treatment is performed immediately before the formation of themedium-protecting layer, the carbon atoms decomposed by plasma can reacha substrate while maintaining the high energy level. Since the carbonatoms maintaining the high energy level are used for forming a film onthe substrate on a magnetic film, a medium-protecting layer with highdensity and high durability can be formed. Furthermore, the heating ofthe magnetic layer at a high temperature enhances the adhesion betweenthe magnetic layer and the medium-protecting layer.

After the formation of the medium-protecting layer, themedium-protecting layer may be further exposed to a nitrogen atmosphereat a flow rate of 100 to 350 sccm for surface treatment. The exposure tothe nitrogen atmosphere at a flow rate of 100 to 350 sccm regulates thenumber ratio (N/C) of nitrogen (N) atoms and carbon (C) atoms to 0.050to 0.150, and the medium-protecting layer formed by CVD is provided withsuitable adhesion to a lubrication layer and suitable hardness.

Furthermore, a lubrication layer containing a perfluoro polyethercompound having a hydroxyl group in an end group may be formed.

The perfluoro polyether has a linear-chain structure and exhibitslubrication performance suitable for the perpendicular magneticrecording medium and also can exhibit high adhesion performance to themedium-protecting layer due to the hydroxyl (OH) group residing in theend group. In particular, in the configuration of the present inventionin which a surface treatment layer containing nitrogen is provided on asurface of the medium-protecting layer, a high adhesion rate of thelubrication layer can be obtained because of the high compatibilitybetween (N⁺) and (OH⁻).

Advantages

As described above, according to the perpendicular magnetic recordingmedium of the present invention, the durability, such as wear resistanceand impact resistance, is enhanced, and various problems, such as highfly write, can be avoided by preventing the pick up of the lubricationlayer material to the magnetic head, even if the thickness of themedium-protecting layer is reduced to 3 nm or less.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a structure of a perpendicular magneticrecording disk according to an embodiment.

FIG. 2 is an explanatory diagram illustrating magnetic characteristicsin an AFC structure.

FIG. 3 is an explanatory diagram showing a relationship between thesubstrate temperature of perpendicular magnetic recording mediacontaining Fe at various concentrations and the intensity of exchangecoupling magnetic fields Hex due to AFC.

FIG. 4 is an explanatory diagram showing a relationship between the Feconcentration and the blocking temperature.

FIG. 5 is an explanatory diagram showing a relationship between the Feconcentration and the saturation magnetization Ms.

FIG. 6 is an explanatory diagram showing a relationship between thesubstrate temperature immediately before the formation of themedium-protecting layer and the peak ratio Dh/Gh after the heating.

FIG. 7 is an explanatory diagram showing a relationship between the Feconcentration and the peak ratio Dh/Gh after the heating.

FIG. 8 is an explanatory diagram showing parameters and effectiveness inexamples and comparative examples.

FIG. 9 is an explanatory diagram illustrating an image of a Ramanspectrum.

FIG. 10 is a plot diagram in which values of N/C and Dh/Gh in theexamples and the comparative examples are plotted.

BEST MODES FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described indetail with reference to the accompanied drawings below. Incidentally,the sizes, materials, and other specific numeric values shown in thefollowing embodiments are only examples provided for betterunderstanding of the invention, and the present invention is not limitedthereto unless otherwise specifically indicated.

FIG. 1 is a diagram illustrating a structure of a perpendicular magneticrecording disk 100 as a perpendicular magnetic recording mediumaccording to an embodiment. The perpendicular magnetic recording disk100 shown in FIG. 1 is configured of a disk substrate 10, an adhesionlayer 12, a first soft magnetic layer 14 a, a spacer layer 14 b, asecond soft magnetic layer 14 c, an orientation control layer 16, afirst under layer 18 a, a second under layer 18 b, an onset layer 20, afirst magnetic recording layer 22 a, a second magnetic recording layer22 b, a capped layer 24, a medium-protecting layer 26, and a lubricationlayer 28. The first soft magnetic layer 14 a, the spacer layer 14 b, andthe second soft magnetic layer 14 c collectively constitute a softmagnetic layer 14. The first under layer 18 a and the second under layer18 b collectively constitute an under layer 18. The first magneticrecording layer 22 a and the second magnetic recording layer 22 bcollectively constitute a magnetic recording layer 22.

First, amorphous aluminosilicate glass was formed into a disk-like shapeby a direct press to produce a glass disk. The glass disk wassuccessively subjected to grinding, polishing, and chemicalstrengthening to obtain a smooth non-magnetic disk substrate 10 made ofa chemically strengthened glass disk.

Since the aluminosilicate glass can provide smoothness and highrigidity, the magnetic spacing, in particular, the flying height of amagnetic head can be reduced more stably. Furthermore, thealuminosilicate glass can be provided with a high degree of rigidity bythe chemical strengthening.

On the resulting disk substrate 10, from the adhesion layer 12 to thecapped layer 24 were successively formed by a DC magnetron sputteringprocess in an Ar atmosphere using a vacuumed film-forming apparatus, andthe medium-protecting layer 26 was formed by a CVD method. Then, thelubrication layer 28 was formed by a dip-coating method. In addition,from the standpoint of enabling the formation of an even film, it isalso preferred to use an in-line type film forming method. Theconfiguration of each layer and a production process thereof will bedescribed in detail below.

The adhesion layer 12 was formed using a Ti-alloy target so as to be aTi-alloy layer of a 10 nm. By forming the adhesion layer 12, theadhesion between the disk substrate 10 and the soft magnetic layer 14can be enhanced and, therefore, it is possible to prevent peeling of thesoft magnetic layer 14. As a material of the adhesion layer 12, forexample, a CrTi alloy can be used. From a practical viewpoint, thethickness of the adhesion layer is preferably set to 1 to 50 nm.

The soft magnetic layer 14 was configured so as to have an AFC bydisposing a non-magnetic spacer layer 14 b between the first softmagnetic layer 14 a and the second soft magnetic layer 14 c. By doingso, the magnetization direction of the soft magnetic layer 14 can bearranged along the magnetic path (magnetic circuit) with high precision,and the vertical component of the magnetization is significantlydecreased, which can reduce the noise generated by the soft magneticlayer 14.

FIG. 2 is an explanatory diagram illustrating magnetic characteristicsin an AFC structure. Referring to such magnetic characteristics, thesoft magnetic layer not having an AFC structure maintains a positivelyor negatively magnetized state when a magnetic field H is not appliedthereto. However, as shown in (b), the soft magnetic layer having an AFCstructure forms closed paths of magnetic fluxes between the first softmagnetic layer 14 a and the second soft magnetic layer 14 c, and themagnetization M becomes 0, when a magnetic field H is not applied. Then,as shown in (a) and (c), the magnetic fluxes of the soft magnetic layers14 a and 14 c are oriented to the same direction by applying a magneticfield H to either direction.

The strength of the coupling of the AFC structure is determined on thebasis of the exchange coupling magnetic field Hex shown in FIG. 2. Ahigher Hex indicates a stronger coupling of AFC. Such Hex is set so asto be magnetized with the magnetic field for writing to thecorresponding magnetic recording layer 22 and so as not to be magnetizedwith the magnetic field for writing to the adjacent magnetic recordinglayer 22. The intensity of the Hex can be increased by reducing thethickness, but a simple reduction in the thickness causes insufficientabsorption of the magnetic flux from the magnetic head. Therefore, thethickness is necessarily reduced according to the magnetic flux from themagnetic head.

The magnetization M of the soft magnetic layer having an AFC structureis increased in accordance with the application of the magnetic field Hto a certain value and then to a saturated state. The value of themagnetization M at the saturated state is called a saturationmagnetization Ms. An increase in the saturation magnetization Msenhances the easiness of write to a recording medium, that is, enhancesthe overwrite characteristics. The saturation magnetization Ms ispreferably 1.2 T or more. By doing so, it is possible to maintaindesired overwrite characteristics.

Furthermore, the magnetic moment indicating the magnetic intensity of amagnetic film is expressed by, Ms·t, the product of the saturationmagnetization Ms and the thickness t of the film. Therefore, in order toobtain a magnetic moment Ms·t of a desired intensity, it is necessary toincrease the thickness of the film when the saturation magnetization Msis low. However, the coupling strength of the AFC is decreased with anincrease in the thickness of a film, resulting in a reduction in Hex.Therefore, it is preferable that the magnetic moment Ms·t of a certainintensity be obtained with a possible maximum saturation magnetizationMs and a possible minimum thickness t.

In the thus configured AFC structure, the coupling of axes of easymagnetization of the upper and the lower two layers disposed inantiparallel to each other is usually destroyed by heat of a certaintemperature or higher. This reduces the S/N ratio. In the embodiment, anAFC structure that is strong to heat is formed by mixing iron to thesoft magnetic layer during the formation thereof. This makes thebelow-described heating immediately before the formation of themedium-protecting layer possible. Therefore, the first soft magneticlayer 14 a and the second soft magnetic layer 14 c each have acomposition of CoCrFeB containing 30 to 70 at % Fe, and the spacer layer14 b has a composition of Ru (ruthenium).

The orientation control layer 16 has an effect of protecting the softmagnetic layer 14 and an effect of enhancing the orientation arrangementof crystalline particles of the under layer 18. The orientation controllayer 16 was a NiW or NiCr layer having an fcc structure.

The under layer 18 has a two-layer structure made of Ru. The crystalorientation properties can be improved by forming the second under layer18 b on the upper layer side under an Ar gas pressure higher than thatfor forming the first under layer 18 a on the lower layer side.

The onset layer 20 is a non-magnetic granular layer. The non-magneticgranular layer is formed on an hcp crystal structure of the under layer18, and then a granular layer as the first magnetic recording layer 22 ais made to grow on the non-magnetic granular layer. This has an effectto separate the magnetic granular layer from the beginning stage(start-up). The composition of the onset layer 20 was non-magneticCoCr—SiO₂.

The magnetic recording layer 22 is configured of a first magneticrecording layer 22 a having a small thickness and a second magneticrecording layer 22 b having a large thickness.

The first magnetic recording layer 22 a was formed so as to have a 2 nmCoCrPt—Cr₂O₃ hcp crystal structure using a hard magnetic target composedof CoCrPt containing chromium oxide (Cr₂O₃) as an example of thenon-magnetic material. The non-magnetic material was segregated at thesurroundings of a magnetic material to form grain boundaries, and themagnetic particles (magnetic grains) formed a columnar granularstructure. The magnetic particles epitaxially grew continuously from thegranular structure of the onset layer.

The second magnetic recording layer 22 b was formed so as to have a 10nm CoCrPt—TiO₂ hcp crystal structure using a hard magnetic targetcomposed of CoCrPt containing titanium oxide (TiO₂) as an example of thenon-magnetic material. In also the second magnetic recording layer 22 b,the magnetic particles formed a granular structure.

The capped layer 24 is a thin film (continuous layer) formed on thegranular magnetic layer and showing a strong perpendicular magneticanisotropy and configures a CGC (coupled granular continuous) structure.By doing so, high thermal fluctuation resistance of the continuous film,in addition to the high-density recording properties and the low-noiseproperties of the granular layer, can be provided. The composition ofthe capped layer 24 was CoCrPtB.

The medium-protecting layer 26 is a medium-protecting layer forprotecting the perpendicular magnetic recording layer from impact of themagnetic head.

In such a medium-protecting layer 26, a metal such as cobalt (Co) isprecipitated from a lower layer to form an oxide thereof on a surface ofthe medium-protecting layer, that is, so-called corrosion occurs. Thecorrosion erases the data recorded at the position where the corrosionoccurred and, in combination with a low flying height of the magnetichead, causes crash failure, which possibly develops into failure in thedisk drive.

In the embodiment, the occurrence of corrosion is inhibited byincreasing the diamond-like bonds by heating the magnetic layerimmediately before the formation of the medium-protecting layer 26 forenhancing the durability, such as wear resistance and impact resistance,of the medium-protecting layer 26. However, the AFC structure of thesoft magnetic layer that is already formed before the formation of themedium-protecting layer 26 is usually weak to heat, and the coupling ofaxes of easy magnetization of the upper and the lower two layersdisposed in antiparallel to each other is destroyed by heating themagnetic layer. Finally, the function as the AFC structure is lost. Inthe embodiment, as described above, an AFC structure containing Fe andthereby being excellent in heat resistance was configured for enablingthe heating of the magnetic layer immediately before the formation ofthe medium-protecting layer 26.

Thus, by heating the magnetic layer immediately before the formation ofthe medium-protecting layer 26, the properties of the medium-protectinglayer 26 formed immediately after the heating are changed. In theembodiment, in particular, the Raman spectrum (the ratio of diamond-likebonds and graphite-like bonds) is changed, and the resistance of themedium-protecting layer 26 is enhanced with an increase in thediamond-like bonds. The heat treatment is conducted such that themedium-protecting layer 26 later formed has a peak ratio Dh/Gh in therange of 0.70 to 0.95.

Here, the peak ratio Dh/Gh is a ratio of Dh and Gh when a Raman spectrumin wavenumbers of 900 to 1800 cm⁻¹ obtained by exciting themedium-protecting layer with argon ion laser light having a 514.5 nmwavelength is measured, background due to fluorescence is amended tostraight-line approximation, and the D peak Dh appearing near the lowerwavenumber side (1350 cm⁻¹) of the spectrum and the G peak Gh appearingnear the higher wavenumber side (1520 cm⁻¹) are waveform-separated by aGaussian function.

When the Dh/Gh is less than 0.70, the hardness of the medium-protectingfilm is insufficient, and a Dh/Gh of 0.95 or more may reduce thehardness of the medium-protecting layer. Therefore, the Dh/Gh iscontrolled to 0.70 to 0.95. By controlling the Dh/Gh within the range of0.70 to 0.95, the medium-protecting layer formed by CVD can havesuitable hardness and sufficient durability.

Specific heating temperature for controlling the peak ratio Dh/Gh to0.70 to 0.95 is, for example, in a temperature range of 157 to 204° C.When the temperature for forming the film is lower than 157° C., thekinetic energy of carbon atoms is low to reduce the density of themedium-protecting layer, and a temperature higher than 204° C. causesdiffusion of the magnetic layer itself to deteriorate the magneticcharacteristics. Accordingly, the temperature of the perpendicularmagnetic recording disk 100 was regulated to 157 to 204° C. immediatelybefore the formation of the medium-protecting layer 26 and after theformation of the magnetic layer. Therefore, the medium-protecting layerhaving high degrees of density and hardness can be formed by heating themagnetic layer to 157 to 204° C.

When the heat treatment is conducted immediately before the formation ofthe medium-protecting layer 26 as described above, during the formationof the medium-protecting layer 26, carbon atoms decomposed by plasmareach the perpendicular magnetic recording disk 100 while maintaining ahigh energy level and are used for the formation of a film. Therefore,the medium-protecting layer 26 can be formed so as to have high densityand high durability. In addition, the heating of the magnetic layer at ahigh temperature enhances the adhesion between the magnetic layer andthe medium-protecting layer.

After such heat treatment, the medium-protecting layer 26 is formed fromcarbon by a plasma CVD method. In the case that the medium-protectinglayer of a hydrocarbon is formed by plasma CVD, it is desirable to formdiamond-like bonds by using only hydrocarbon gas as the reactive gas.This is because that if another inert gas (for example, Ar) or a carriergas such as hydrogen gas is used by being mixed with hydrocarbon gas,such impure gas is incorporated into the medium-protecting layer andreduces the film density.

Incidentally, as the reactive gas, a hydrocarbon (carbon hydride), inparticular, a lower hydrocarbon is preferably used, and a straight-chainlower saturated hydrocarbon or a straight-chain lower unsaturatedhydrocarbon is more preferably used. As the straight-chain lowersaturated hydrocarbon, for example, methane, ethane, propane, butane,pentane, hexane, heptane, or octane may be used. As the straight-chainlower unsaturated hydrocarbon, for example, ethylene, propylene,butylene, or acetylene may be used. In addition, the term “lower” usedherein means a hydrocarbon having 1 to 10 carbon atoms per molecule.

In accordance with an increase in the number of carbon atoms, it becomesdifficult to gasify the hydrocarbon and supply the gasified hydrocarbonto a film-forming apparatus, and also decomposition during the plasmadischarging becomes difficult. Accordingly, the straight-chain lowerhydrocarbon is preferably used.

In addition, in accordance with an increase in the number of carbonatoms, the component of the resulting medium-protecting layer is proneto contain a large amount of high-molecular hydrocarbons and reduces thedensity and the hardness of the medium-protecting layer. Furthermore, itis cited that cyclic hydrocarbons are difficult to be decomposed duringthe plasma discharging, compared to straight-chain hydrocarbons.Therefore, the hydrocarbon is preferably a straight-chain lowerhydrocarbon, and, in particular, the use of ethylene enables forming amedium-protecting layer having high degrees of density and hardness.

In general, since the film hardness of a carbon film formed by the CVDmethod is enhanced compared to a film formed by a sputtering process,the perpendicular magnetic recording layer can be more effectivelyprotected from impact from the magnetic head.

Furthermore, after the formation of the film by the CVD method, themedium-protecting layer 26 is exposed to a nitrogen atmosphere at a flowrate of 100 to 350 sccm for surface treatment such that the number ratio(N/C) of nitrogen (N) atoms and carbon (C) atoms is 0.050 to 0.150.Here, when the N/C is smaller than 0.05, high fly write frequentlyoccurs to cause errors in the recording/reproduction process, and an N/Cof larger than 0.150 has a high possibility of crash. Accordingly, theN/C is regulated to be 0.05 to 0.15. Therefore, by regulating the N/C inthe range of 0.05 to 0.15, the medium-protecting layer formed by CVD canhave suitable adhesion to a lubrication layer and suitable hardness.

Here, the number ratio (N/C) of nitrogen atoms to carbon atoms can bemeasured using an X-ray photoelectron spectroscopy (hereinafter calledESCA (electron spectroscopy for chemical analysis)). Details are thatthe number ratio of nitrogen atoms to carbon atoms is determined on thebasis of the intensities of N1s spectrum and C1s spectrum measured byESCA.

In the embodiment, the thickness of the medium-protecting layer 26 ispreferably 1 nm or more. A thickness of smaller than 1 nm reduces thecoverage of the medium-protecting layer 26 and may be thereforeinsufficient for preventing the migration of metal ions of the magneticlayer and further may cause a problem in wear resistance. It is notparticularly necessary to determine an upper limit in the thickness ofthe medium-protecting layer formed by CVD, but the thickness ispreferably set to 3 nm or less from a practical viewpoint not to preventthe improvement in magnetic spacing.

Furthermore, it is preferable to apply a bias voltage of −300 to −50 Vwhen the medium-protecting layer 26 is formed. When the voltage is lowerthan −300 V, an excessive energy is applied to a substrate to causearcing, which is responsible for particles and contamination. On theother hand, when the voltage is higher than −50 V, the effect of thebias application does not appear. Accordingly, the application voltageis determined to −300 to −50 V.

Then, after the formation of the medium-protecting layer 26, the surfacequality of the perpendicular magnetic recording disk 100 can be enhancedby washing with ultrapure water and isopropyl alcohol.

Because of the above-described medium-protecting layer 26, problems in,for example, load unload (hereinafter simply referred to as LUL)durability do not occur even if the thickness of the medium-protectinglayer is 3 nm or less, though conventionally produced productions havingthicknesses of 3 nm or less cause durability abnormality such as scratchand deterioration of, for example, the reproduced signals in high flywrite.

The lubrication layer 28 was formed by dip-coating PFPE (perfluoropolyether). The thickness of the lubrication layer 28 is about 1 nm. Bythe effect of the lubrication layer 28, the medium-protecting layer 26can be prevented from damage or chipping even if the magnetic head isbrought into contact with the surface of the perpendicular magneticrecording disk 100. The perfluoro polyether has a linear-chain structureand exhibits lubrication performance suitable for the perpendicularmagnetic recording disk and also can exhibit high adhesion performanceto the medium-protecting layer 26 due to the hydroxyl (OH) groupprovided in the end group. In particular, in the configuration of theembodiment in which a surface treatment layer containing nitrogen isprovided on a surface of the medium-protecting layer, since (N⁺) and(OH⁻) have high affinity to each other, a high adhesion rate of thelubrication layer can be obtained, which is preferable.

In addition, as the perfluoro polyether compound having a hydroxyl groupin the end group, the number of the hydroxyl group is preferably two tofour per molecule. This is because that when the number is smaller thantwo, the adhesion rate of the lubrication layer may be decreased, andwhen the number is greater than four, the lubrication performance may bereduced as a result of the adhesion rate that is too increased. Thethickness of the lubrication layer may be properly controlled in therange of 0.5 to 1.5 nm. This is because that a thickness smaller than0.5 nm may reduce the lubrication performance and that a thicknessgreater than 1.5 nm may reduce the adhesion rate of the lubricationlayer.

The surface roughness, as the Rmax, of the thus produced perpendicularmagnetic recording disk 100 is preferably 2.5 nm or less. This isbecause that a roughness greater than 2.5 nm may inhibit the reductionof the magnetic spacing. The surface roughness is specified in JapaneseIndustrial Standards (JIS) BO601.

According to the production process above, the perpendicular magneticrecording disk 100 was obtained. The grounds for the above-describedparameters are shown below.

As described above, in the AFC structure in the soft magnetic layer 14,the axes of easy magnetization of the upper and the lower two layersdisposed in antiparallel to each other are usually destroyed by heat ofa certain temperature or higher. This reduces the S/N ratio. However, anAFC structure that is strong to heat is formed by mixing iron to thesoft magnetic layer during the formation thereof. This makes it possibleto perform the below-described heating immediately before the formationof the medium-protecting layer.

FIG. 3 is an explanatory diagram showing a relationship between thesubstrate temperature of the perpendicular magnetic recording disks 100containing Fe at various concentrations and the intensity of exchangecoupling magnetic fields Hex due to AFC. Referring to FIG. 3, it is seenthat when the substrate temperature exceeds a certain temperature, theHex intensity is sharply reduced not to function as the AFC structure.The temperature at such a boundary point (the below-described blockingtemperature) varies depending on the Fe concentration, and the boundarytemperature increases with the Fe concentration.

For example, the boundary temperature of CoTaZr not containing Fe isabout 177° C. The boundary temperature of FeCoTaZr containing 40 at % Feis about 197° C., and that of FeCoBCr containing 65 at % Fe is about210° C. The boundary temperature has a certain degree of regularityregardless of the composition of the material that binds to Fe.

FIG. 4 is an explanatory diagram showing a relationship between the Feconcentration and the blocking temperature (boundary temperature).Referring to FIG. 4, it is seen that the blocking temperatures of theabove-mentioned CoTaZr, FeCoTaZr, and FeCoBCr can be approximatelylinearized so as to be proportional to the Fe concentration and that thetemperature heating the perpendicular magnetic recording disk 100 can beincreased by increasing the Fe concentration. Here, the blockingtemperature (blocking temperature) is a temperature at which the Hexstarts to decrease.

In the embodiment, the blocking temperature can be increased up to about190 to 215° C. by adding 30 to 70 at % Fe to the soft magnetic layer 14.

FIG. 5 is an explanatory diagram showing a relationship between the Feconcentration and the saturation magnetization Ms. Referring to FIG. 5,it is seen that the soft magnetic layer 14 has a saturationmagnetization of 1.2 T or more even if the soft magnetic layer 14contains 30 to 70 at % Fe. In addition, when the soft magnetic layer 14contains 65% Fe, the peak of the saturation magnetization Ms is themaximum value 1.60. This reveals that the soft magnetic layer 14containing 30 to 70 at % Fe has sufficient overwrite characteristics.

Then, the relationship between the heat treatment immediately before theformation of the medium-protecting layer 26 and the peak ratio Dh/Ghafter the heating will be described.

FIG. 6 is an explanatory diagram showing a relationship between thesubstrate temperature immediately before the formation of themedium-protecting layer 26 and the peak ratio Dh/Gh after the heating.As understood by referring to FIG. 6, the peak ratio Dh/Gh graduallyincreases as a function to the substrate temperature, that is, anincrease in the substrate temperature increases the peak ratio Dh/Gh, inother words, increases the number of diamond-like bonds. This enhancesthe resistance of the medium-protecting layer 26.

The preferred value of the peak ratio Dh/Gh in the embodiment is 0.70 to0.95 as described above. It can be comprehended by referring to FIG. 6that the substrate temperature for achieving such the peak ratio Dh/Ghis 157 to 204° C.

FIG. 7 is an explanatory diagram showing a relationship between the Feconcentration and the peak ratio Dh/Gh after the heating. As shown inFIG. 7, when the Fe content in the soft magnetic layer 14 is less than30 at % or higher than 70 at %, the saturation magnetization Ms of thesoft magnetic layer 14 is low not to satisfy the requirement of asaturation magnetization Ms of 1.2 T. Therefore, the perpendicularmagnetic recording disk 100 having such the soft magnetic layer 14cannot maintain the required overwrite characteristics. In addition,when the Fe content is 70% or more, corrosion characteristics aresignificantly reduced not to be used as a medium.

Furthermore, when the peak ratio Dh/Gh is smaller than 0.70, thehardness of the medium-protecting layer 26 is too low. Therefore, thescratches are easily formed, and the reliability of the perpendicularmagnetic recording disk 100 is reduced. Similarly, when the peak ratioDh/Gh is larger than 0.95, the hardness of the medium-protecting layer26 is too high. Therefore, the brittleness is increased, and thereliability of the perpendicular magnetic recording disk 100 is reduced.

Accordingly, when the Fe content in the soft magnetic layer 14 is 30 to70 at % and the peak ratio Dh/Gh of the medium-protecting layer 26 iscontrolled within the range of 0.70 to 0.95, a perpendicular magneticrecording disk 100 having sufficient overwrite characteristics and beingexcellent in reliability can be obtained.

The effectiveness of the embodiment will be described referring to thefollowing examples and comparative examples.

FIG. 8 is an explanatory diagram showing parameters and effectiveness inthe examples and the comparative examples. Here, in thirteen examplesand eight comparative examples, an LUL durability test, a pin-on-disktest, and a high fly write test are performed for evaluatingeffectiveness.

Here, an amorphous glass substrate was used as the substrate 10. Thecomposition thereof is aluminosilicate. The glass substrate was asubstrate for a 2.5-inch-type perpendicular magnetic recording diskhaving a diameter of 65 mm, an inner diameter of 20 mm, and a diskthickness of 0.635 mm. Here, the surface roughness of the resultingglass substrate was observed with an AFM (atomic force microscope) toconfirm that the glass substrate had a smooth surface having an Rmax of2.18 nm and an Ra of 0.18 nm.

Then, an adhesion layer 12, a soft magnetic layer 14, an orientationcontrol layer 16, an under layer 18, an onset layer 20, a magneticrecording layer 22, and a capped layer 24 were sequentially formed onthe substrate 10 by DC magnetron sputtering with a C3040 sputteringmachine manufactured by Canon Anelva Corp. The vacuum pressure duringthe film formation was 0.6 Pa. Detailed description of the filmformation is as follows.

The under layer 18 made of Pd and having a thickness of 7 nm was formedby sputtering on the orientation control layer 16 using Pd as thesputtering target. The vacuum pressure during the film formation was 1.0Pa.

The magnetic recording layer 22 with a 15 nm thickness made of aCoCrPt—TiO₂ alloy was formed by sputtering on the onset layer 20 using asputtering target composed of a CoCrPt—TiO₂ (Cr: 12 at %, Pt: 10 at %,TiO₂: 9 at %, remainder: Co) alloy as the sputtering target. The vacuumpressure during the film formation was 3.5 Pa.

Furthermore, the surface of the perpendicular magnetic recording disk100 after the formation of the capped layer 24 was preheated. Forexample, in Example 1, the perpendicular magnetic recording disk 100 washeated such that the surface temperature of the perpendicular magneticrecording disk 100 became 160° C. by a heating method using a heater.The heating time is about 5 seconds. In addition, the substratetemperature of the perpendicular magnetic recording disk 100 wasconfirmed immediately after the formation of the magnetic layer from awindow of a chamber using a radiation thermometer.

Furthermore, a medium-protecting layer 26 was formed on the disk thatwas formed till the magnetic recording layer 22 by a plasma CVD methodby introducing ethylene gas at 250 sccm under a vacuum pressure of 1 Paand an applied bias voltage of −300 V. The film-forming rate for formingthe medium-protecting layer 26 was 1 nm/sec.

Furthermore, after the formation of the medium-protecting layer 26, themedium-protecting layer 26 was exposed to a nitrogen atmosphere under apressure controlled to a vacuum pressure of 3 Pa by introducing onlynitrogen gas at 250 sccm into the plasma. Thus, treatment forimpregnating the surface of the medium-protecting layer 26 with nitrogenwas conducted.

After the formation of the medium-protecting layer 26, the thickness ofthe medium-protecting layer 26 was measured by cross-section observationwith a transmission electron microscope (TEM). The thickness of themedium-protecting layer 26 was 3.0 nm.

In addition, after the formation of the medium-protecting layer 26, thenumber ratio (N/C) of nitrogen atoms to carbon atoms of themedium-protecting layer 26 was confirmed by ESCA. The value was 0.107.The measurement conditions of the ESCA analysis are as follows:

Apparatus: Quantum2000 manufactured by Ulvac-Phi Inc.,

X-ray excitation source: Al—Kα ray (1486.6 eV),

X-ray source: 20 W,

Vacuum pressure of analysis chamber: <2×10⁻⁷ Pa,

Pass energy: 117.5 eV,

Photoelectron detection angle: 45°,

Measurement subject peak: C1s and N1s,

Analysis region: 100 um φ, and

Cumulated number: ten times.

In addition, Raman spectroscopic analysis after the formation of themedium-protecting layer 26 showed a Dh/Gh of 0.80.

In addition, the Raman spectroscopic analysis was performed byirradiating the surface of the medium-protecting layer 26 with Ar ionlaser having a wavelength of 514.5 nm and observing the Raman spectrumdue to Raman scattering appearing in a wavenumber band of 900 to 1800cm⁻¹.

FIG. 9 is an explanatory diagram illustrating an image of a Ramanspectrum. Here, in the wavenumber range of 900 to 1800 cm⁻¹ of the Ramanspectrum, background due to fluorescence was amended to straight-lineapproximation, and the peak height ratio of the D peak to the G peak wasdetermined as the Dh/Gh.

The Raman spectroscopic analysis is usually conducted before theapplication of the lubrication layer 28, but the Raman spectrum may bemeasured after the application of a lubricant. The Raman spectroscopicanalysis conducted before and after the application of a lubricantshowed that the Dh/Gh values were exactly the same before and after theapplication and revealed that the perfluoro polyether-based lubricationlayer having hydroxyl groups in the end groups did not affect the Ramanspectroscopic analysis.

After the formation of the medium-protecting layer 26, immersioncleaning in pure water at 70° C. was conducted for 400 seconds, and thenwashing with IPA was further conducted for 400 seconds. As finishingdrying, drying with IPA vapor was conducted.

Then, on the medium-protecting layer 26 washed with ultrapure water andIPA, a lubrication layer 28 made of a PFPE (perfluoro polyether)compound was formed by a dip method. Specifically, an alcohol denaturedFomblin Z derivative manufactured by Ausimont Co., Ltd. was used. Thecompound has one or two hydroxyl groups on each end of a main chain ofPFPE, that is, the compound has two to four hydroxyl groups per moleculein the end groups. The thickness of the lubrication layer 28 was 1.4 nm.

As in above, the produced perpendicular magnetic recording disk 100 wasobserved for the surface roughness with an AFM to confirm that thesurface had an Rmax of 2.30 nm and a Ra of 0.22 nm and was smooth. Inaddition, the glide height was measured to be 3.2 nm. When the flyingheight of the magnetic head is stably set to 10 nm or less, it isdesirable that the glide height of the perpendicular magnetic recordingdisk 100 be set to 4.0 nm or less.

The perpendicular magnetic recording disk 100 obtained as mentionedabove was evaluated and analyzed for the various performances thereof inthe following manner.

(Lul Durability Test)

An LUL durability test was conducted using a 2.5-inch-type HDD beingrotated at 5400 rpm and a magnetic head having a flying height of 10 nm.Incidentally, an NPAB (negative-pressure type) slider was used as aslider of the magnetic head, and a TMR type element loaded with a DFHmechanism was used as a reproducing element. The perpendicular magneticrecording disk 100 was loaded on the HDD, and LUL operation wascontinuously performed by the above-described magnetic head.

Then, the LUL durability of the perpendicular magnetic recording disk100 was evaluated by measuring the endurable number of LUL withoutcausing breakdown in the HDD. The environment for conducting the testwas 70° C./80% RH, which is a severer condition than usual HDD operatingenvironment. This is for more adequately determining the endurancereliability of the perpendicular magnetic recording disk 100 byconducting the test under the environment operating an HDD that issupposed to be used in, for example, a car navigation system.

In the LUL durability test, the perpendicular magnetic recording disk100 in each of Examples 1 to 13 exhibited the number of LUL greater than1×10⁶ times without causing breakdown thereof. Usually, in the LULdurability test, it is required that the number of continuous LUL notcausing breakdown be greater than 4×10⁵ times. The number of LUL of4×10⁵ times is comparable to the use of about 10 years under the usualenvironment operating HDDs.

(Pin-on-Disk Test)

The pin-on-disk test was conducted as follows. That is, in order toevaluate the durability and the wear resistance of the medium-protectinglayer 26, the perpendicular magnetic recording disk 100 was rotatedwhile a 2 mm diameter ball made of Al₂O₃—TiC was pressed at a load of 15g to the medium-protecting layer 26 at a position corresponding to 22 mmin radius of the perpendicular magnetic recording medium for rotativelysliding the Al₂O₃—TiC ball at a relative velocity of 2 m/sec withrespect to the medium-protecting layer 26. The number of slidingrotations until the occurrence of breakage in the medium-protectinglayer 26 caused by the sliding was measured.

In the pin-on-disk test, if the number of the sliding rotations untilthe occurrence of breakage in the medium-protecting layer 26 is 300 ormore, it is determined to pass the test. In addition, usually, themagnetic recording head is not brought into contact with theperpendicular magnetic recording disk 100. Therefore, this pin-on testis a durability test under severe environment compared to actualenvironment for use. For example, the number of the sliding rotations ofthe perpendicular magnetic recording disk 100 of Example 1 was 501times, and those in all other examples were higher than 300 times.

(High Fly Write Test)

The high fly write test was conducted as follows. A 2.5-inch-type HDDthat rotates at 5400 rpm and a magnetic head with a flying height of 10nm are used. In addition, an NPAB (negative-pressure type) slider wasused as a slider of the magnetic head, and a TMR type element loadedwith a DFH mechanism was used as a reproducing element. Theperpendicular magnetic recording disk 100 was loaded on the HDD, and theDFH mechanism was operated to generate heat in the head element. Themagnetic head was thermally expanded with the heat to protrude in theABS direction by 2 nm. Under this state, recording/reproduction wasconducted for 1000 hours, and occurrence of failure by error wasinvestigated. As a result, error did not occur in therecording/reproduction for 1000 hours in Examples 1 to 13.

The comparative examples were also subjected to the LUL durability test,the pin-on-disk test, and the high fly write test as in theabove-described examples.

For example, in Comparative Example 1, a perpendicular magneticrecording disk was formed as in Example 1 except that themedium-protecting layer 26 was exposed to nitrogen gas at 90 sccm.However, since the amount of introduced nitrogen was too small, in thehigh fly write test, the failure that no recording/reproduction wasperformed occurred 12 hours after the starting.

In addition, in Comparative Example 2, since the exposure to nitrogengas at 360 sccm was conducted, the amount of introduced nitrogen was toolarge. Therefore, the specification, 300 times, in the pin-on test disktest was not achieved, and scratches occurred in the perpendicularmagnetic recording disk in the LUL test to cause crash at 3×10⁵ times.It can be understood that other comparative examples do not satisfyacceptable values of one or a plurality of the LUL durability test, thepin-on-disk test, and the high fly write test when one or a plurality ofparameters are different from those in Example 1 and deviate frompredetermined ranges.

FIG. 10 is a plot diagram in which values of N/C and Dh/Gh in theexamples and the comparative examples are plotted. As seen by referringthe examples in the N/C range of 0.050 to 0.150 and the Dh/Gh range of0.70 to 0.95 indicated by a solid-line square in the drawing and thecomparative examples outside the range, the perpendicular magneticrecording disks 100 according to the embodiment can be also applied to aDFH head and can avoid high fly write failure even if the thickness ofthe medium-protecting layer is 3 nm or less and further have suitablewear resistance and sliding characteristics. In addition, it is obviousthat the perpendicular magnetic recording disk 100 according to theembodiment can be applied to an HDD of an LUL system.

As in above, the preferred examples of the present invention have beendescribed referring to the accompanied drawings, but it is obvious thatthe present invention is not limited to such examples. It is evidentthat those skilled in the art can arrive at various alterations andmodifications within the scope described in Claims, and it is understoodthat those alterations and modifications surely belong to the technicalscope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention can be used in a perpendicular magnetic recordingmedium that is loaded on, for example, an HDD and in a process ofproducing the medium.

1. A perpendicular magnetic recording medium comprising a magneticrecording layer on a substrate, and a medium-protecting layer on themagnetic recording layer, wherein the magnetic recording layer is aferromagnetic layer of a granular structure having grain boundariesformed by a non-magnetic material among crystalline particles grown in acolumnar shape and containing at least cobalt (Co); and themedium-protecting layer is composed of a coating that includes carbon asa main component and nitrogen contained in a surface layer at a numberratio (N/C) of nitrogen (N) atoms and carbon (C) atoms of 0.050 to0.150, and in a spectrum removed fluorescence from a Raman spectrum inwavenumbers of 900 to 1800 cm⁻¹ obtained by exciting themedium-protecting layer with argon ion laser light having a 514.5 nmwavelength, a peak ratio Dh/Gh when a D peak Dh appearing near 1350 cm⁻¹and a G peak Gh appearing near 1520 cm⁻¹ are waveform-separated by aGaussian function is 0.70 to 0.95.
 2. The perpendicular magneticrecording medium according to claim 1, further comprising a softmagnetic layer below the magnetic recording layer, wherein the softmagnetic layer is formed so as to have an antiferromagnetic exchangecoupling (AFC) structure containing 30 to 70 at % iron (Fe) and has asaturation magnetization Ms of 1.2 T or more.
 3. The perpendicularmagnetic recording medium according to claim 2, wherein the softmagnetic layer has an exchange coupling magnetic field Hex of 40O e ormore.
 4. The perpendicular magnetic recording medium according to claim1, further comprising a capped layer on the magnetic recording layer,wherein the magnetic recording layer is formed so as to have a granularstructure.
 5. The perpendicular magnetic recording medium according toclaim 4, wherein the capped layer has a composition of CoCrPtB.
 6. Amethod of manufacturing a perpendicular magnetic recording mediumincluding a magnetic recording layer on a substrate, and amedium-protecting layer composed of a coating including carbon as a maincomponent on the magnetic recording layer, comprising: forming aferromagnetic layer of a granular structure having grain boundariesformed by a non-magnetic material among crystalline particles grown in acolumnar shape and containing at least cobalt (Co), as the magneticrecording layer; heating the perpendicular magnetic recording mediumsuch that in a spectrum removed fluorescence from a Raman spectrum of amedium-protecting layer formed later in wavenumbers of 900 to 1800 cm⁻¹obtained by exciting the medium-protecting layer with argon ion laserlight having a 514.5 nm wavelength, a peak ratio Dh/Gh when a D peak Dhappearing near 1350 cm⁻¹ and a G peak Gh appearing near 1520 cm⁻¹ arewaveform-separated by a Gaussian function is 0.70 to 0.95; forming themedium-protecting layer by a CVD method; and exposing themedium-protecting layer with nitrogen such that the number ratio (N/C)of nitrogen (N) atoms and carbon (C) atoms is 0.050 to 0.150.
 7. Themethod of manufacturing the perpendicular magnetic recording mediumaccording to claim 6, further comprising: forming a soft magnetic layerof an antiferromagnetic exchange coupling (AFC) structure containing 30to 70 at % iron (Fe) before the formation of the magnetic recordinglayer.
 8. The method of manufacturing the perpendicular magneticrecording medium according to claim 7, wherein the soft magnetic layerhas an exchange coupling magnetic field Hex of 40O e or more.
 9. Themethod of manufacturing the perpendicular magnetic recording mediumaccording to claim 6, further comprising: forming a capped layer of agranular structure after the formation of the magnetic recording layer.10. The method of manufacturing the perpendicular magnetic recordingmedium according to claim 9, wherein the capped layer has a compositionof CoCrPtB.
 11. The method of manufacturing the perpendicular magneticrecording medium according to claim 6, wherein the heating is performedat a temperature of 157 to 204° C.
 12. The method of manufacturing theperpendicular magnetic recording medium according to claim 6, furthercomprising: exposing to a nitrogen atmosphere at a flow rate of 100 to350 sccm so as to surface-treat the medium-protecting layer afterforming the medium-protecting layer.
 13. The method of manufacturing theperpendicular magnetic recording medium according to claim 6, furthercomprising: forming a lubrication layer containing a perfluoro polyethercompound having a hydroxyl group in an end group.